Coated carrier for developing electrostatically charged images

ABSTRACT

This invention relates to a coated carrier for development of an electrostatically charged image, comprising carrier core particles coated with a coating resin; wherein the coating resin at least includes a polyolefin resin having a cyclic structure; a polyolefin resin of a cyclic structure having an intrinsic viscosity (i.v.) of 0.25 dl/g or more, a heat distortion temperature (HDT) by DIN53461-B of 70 ° C. or higher, and a number average molecular weight of 7,500 or more and a weight average molecular weight of 15,000 or more, as measured by GPC, is contained in an amount of less than 50% by weight based on the entire coating resin; and the coating resin is used for coating in an amount of 1 to 30% by weight based on the carrier core particles. The present invention can obtain a coated carrier which exhibits high anti-spent toner effect and excellent charge control properties during development with a dry toner.

TECHNICAL FIELD

The present invention relates to a coated carrier for development of anelectrostatically charged image. More specifically, this inventionprovides a coated carrier having a satisfactory anti-spent toner effectand excellent charge control properties when developing anelectrostatically charged image with a dry toner, thereby providing asharp and stable image.

BACKGROUND ART

Electrostatically charged image development type copiers and printersare gaining popularity because of widespread office automation. Withthis background, demand is growing for high grade or sharp, stablecopied or printed images. General formulations for carriers inelectrostatically charged image developing copiers and printers areshown in Table 1. One of the main factors for improving the sharpnessand stability of a copy image is a surface coating resin of the carrier.An electrostatically charged image developing copier or printer feeds atoner to an electrostatically charged image on a latent image carrier toobtain a visible image, then transfers the resulting toner image to aplain paper or an OHP film, and fixes the transferred image. Currently,developers comprising toner particles electrostatically joined tocarrier particles of iron powder or carrier particles of ferriteconsisting essentially of nickel or cobalt are in wide use as means ofsupplying toner to the electrostatically charged image on the latentimage carrier to obtain the visible image. For the surface of thesecarriers, fluoro-acrylic graft polymer, cellulose butyl acetate, orsilicone resin is used as a coating material to impart charge controlproperties and anti-spent toner effect (spent toner phenomenon is aphenomenon in which the toner adhering to the surface of the carrier isfirmly bonded to the carrier electrostatically, physically orchemically, and thus the toner is not transferred to theelectrostatically charged image on the latent image carrier). Thecoating material proves satisfactory in a copy image initially formed.During its long-term use, however, toner particles that havetriboelectrically adhered to carrier particles become difficult toseparate from the carrier owing to the accumulation of electrostaticcharges between the toner and the carrier. Alternatively, the adheringtoner particles are fusion bonded to the carrier surface because of heatof friction, so that the replenishing toner is not charged. As a result,replenishment of toner to the electrostatically charged image on thelatent image carrier is insufficient, causing image deterioration,namely, short life of the developer.

                  TABLE 1                                                         ______________________________________                                                              (% by weight)                                             Core substance Surface coating agent                                        ______________________________________                                        Iron oxide powder                                                                         Iron oxide powder                                                                           1-30                                                  type carrier 70-99                                                            Ferrite type Ferrite powder 1-30                                              carrier 70-99                                                               ______________________________________                                    

The present invention has been accomplished in the light of theaforementioned problems. The object of this invention is to provide acoated carrier which is capable for achieving a higher grade copy image,that is, a sharp image, and a long life of the developer, in anelectrostatically charged image development type copier or printer.

DISCLOSURE OF THE INVENTION

A first aspect of the present invention is to provide a coated carrierfor development of an electrostatically charged image, the coatedcarrier comprising carrier core particles coated with a coating resin;wherein

the coating resin at least includes a polyolefin resin having a cyclicstructure;

a polyolefin resin of a cyclic structure having an intrinsic viscosity(i.v.) of 0.25 dl/g or more, a heat distortion temperature (HDT) byDIN53461-B of 70° C. or higher, and a number average molecular weight of7,500 or more and a weight average molecular weight of 15,000 or more,as measured by GPC, is contained in an amount of less than 50% by weightbased on the entire coating resin; and

the coating resin is used for coating in an amount of 1 to 30% by weightbased on the carrier core particles.

A second aspect of the invention is to provide the coated carrier fordevelopment of an electrostatically charged image regarding the firstaspect of the invention, wherein the coating resin consists of 1 to 100parts by weight of a polyolefin resin having a cyclic structure, and 0to 99 parts by weight of at least one resin selected from fluoroacrylicgraft polymer, cellulose butyl acetate, and silicone resins.

A third aspect of the invention is to provide the coated carrier fordevelopment of an electrostatically charged image according the first orsecond aspect of the invention, wherein the polyolefin resin having acyclic structure has at least one functional group selected from acarboxyl group, a hydroxyl group and an amino group.

A fourth aspect of the invention is to provide the coated carrier fordevelopment of an electrostatically charged image regarding the first,second or third aspect of the invention, wherein the polyolefin resinhaving a cyclic structure is an ionomer, or has a structure crosslinkedwith dienes.

To solve the aforementioned problems, we, the inventors, have worked outa measure covering the use of a resin with excellent charge controlproperties, satisfactory surface lubricating properties, and high rubresistance. Examples of such a resin are fluoro-acrylic graft polymer,cellulose butyl acetate, and silicone resins. These resins, however, areknown to be unsatisfactory in terms of the properties required ofcarrier surface coating resins, such as charge control properties,surface lubricating properties, and rub resistance, and to bequestionable when used as coating resins. We have conducted extensivestudies to correct these drawbacks, and have found that a carrierproviding a high grade image and a long life developer can be producedby using a colorless, transparent polyolefin resin of a cyclic structurewhich can satisfy the charge control properties, surface lubricatingproperties, and rub resistance, wherein the polyolefin resin containsless than 50% by weight of a high-viscosity resin based on the entirecoating resin. This finding has led us to accomplish the presentinvention. A carrier using as a carrier surface coating resin apolyolefin resin of a cyclic structure fulfilling these characteristicsimparts excellent anti-spent toner effect and charge control properties.The use of a developer using this carrier has been found to achieve ahigh grade, sharp image.

The carrier for development of an electrostatically charged image of thepresent invention has a coating resin, wherein the coating resin atleast includes a polyolefin resin having a cyclic structure, and apolyolefin resin of a cyclic structure having an intrinsic viscosity(i.v.) of 0.25 dl/g or more, a heat distortion temperature (HDT) byDIN53461-B of 70° C. or higher, and a number average molecular weight of7,500 or more and a weight average molecular weight of 15,000 or more,as measured by GPC, is contained in an amount of less than 50% by weightbased on the entire coating resin.

The polyolefin resin having a cyclic structure used herein is, forexample, a copolymer of an alpha olefin, such as ethylene, propylene orbutylene, with an alicyclic compound having a double bond, such ascyclohexene or norbornene, which copolymer is colorless and transparent,and has high light transmittance. This polyolefin having a cyclicstructure is a polymer obtained, for instance, by a polymerizationmethod using a metallocene catalyst or a Ziegler catalyst.

Preferred as the colorless, transparent polyolefin resin of a cyclicstructure with satisfactory charge control properties, surfacelubricating properties and rub resistance used in the present inventionare a low-viscosity resin having a number average molecular weight of1,000 to 7,500, preferably 3,000 to 7,500, and a weight averagemolecular weight of 1,000 to 15,000, preferably 4,000 to 7,500, asmeasured by GPC, an intrinsic viscosity (i.v.) of less than 0.25 dl/g,and a heat distortion temperature (HDT) by DIN53461-B of lower than 70°C., and a high-viscosity resin having a number average molecular weightof 7,500 or more, preferably 7,500 to 50,000, and a weight averagemolecular weight of 15,000 or more, preferably 15,000 to 100,000, asmeasured by GPC, an i.v. of 0.25 dl/g or more, and an HDT of 70° C. orhigher.

The high-viscosity polyolefin resin having a cyclic structure has theaforesaid properties. Compared with the same resin with a low viscosity,therefore, this resin can improve the mechanical strength, such as rubresistance, of the resulting carrier coating, and also ensures theadhesion strength of the coating onto the carrier particles. However, ifthe proportion of the high-viscosity polyolefin resin having a cyclicstructure is 50% or more, the anti-spent toner properties will beimpaired.

In the present invention, a coated carrier using a coating resincomprising a mixture of other resin with the polyolefin resin having acyclic structure, which satisfies the foregoing characteristics, alsoachieves a high grade, sharp image. In this case, it is preferred thatthe proportions of the polyolefin resin having a cyclic structure andthe other resin in the coating resin is to be 1 to 100, preferably 20 to90, more preferably 50 to 90 parts by weight of the former, and 0 to 99,preferably 10 to 80, more preferably 10 to 50 parts by weight of thelatter. If the amount of the former resin is less than 1 part by weight,it becomes difficult to obtain a high grade image and a long-lifedeveloper.

If a carboxyl group is introduced into the polyolefin resin having acyclic structure by the melt air oxidation method or modification withmaleic anhydride, its compatibility with the other resin and thedispersibility of the pigment can be improved. The same improvement canbe achieved by introducing a hydroxyl group or an amino group by a knownmethod.

Furthermore, the rub resistance and the anti-spent toner properties canbe further improved by copolymerizing the polyolefin resin having acyclic structure with a diene monomer such as norbornadiene orcyclohexadiene, or by introducing a crosslinking structure into thepolyolefin resin of a cyclic structure, which has a carboxyl groupintroduced therein, by adding a metal such as zinc, copper or calcium.

In the present invention, the polyolefin resin having a cyclic structureis coated as a surface coating agent onto carrier core particlescomprising iron powder or ferrite. The amount of the coating polyolefinresin is 1 to 30% by weight based on the carrier core particles, and themethod of coating is by such means as a spray dryer. If the amount ofthe coating is less than 1% by weight, the surface of the carrier cannotbe fully coated, thereby lowering the anti-spent toner effect. If theamount of the coating is more than 30% by weight, stable charge controlproperties are not obtained. A developer using the coated carrier of thepresent invention gives a sharp image and long-term stability of imagequality.

For the toner comprising of the coated carrier of the present inventionand a developer, the particles are used, which consist essentially of abinder resin, a coloring agent, a charge control agent and otheradditives added thereto, where necessary.

As the binder resin there may be used any known ones. Examples includehomopolymers of styrene and its substituted compounds, such aspolystyrene, poly p-chlorostyrene and polyvinyltoluene; styrenecopolymers, such as styrene-p-chlorostyrene copolymer, styrene-propylenecopolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalenecopolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylatecopolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylatecopolymer, styrene-methyl methacrylate copolymer, styrene-ethylmethacrylate copolymer, styrene-butyl methacrylate copolymer,styrene-methyl a-chloromethacrylate copolymer, styrene-acrylonitrilecopolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethylether copolymer, styrene-vinyl methyl ketone copolymer,styrene-butadiene copolymer, styrene-isoprene copolymer,styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer,and styrene-maleic acid ester copolymer; polymethyl methacrylate;polybutyl methacrylate; polyvinyl chloride; polyvinyl acetate;polyethylene; polypropylene; polyesters; polyurethanes; polyamides;epoxy resins; polyvinyl butyral; polyacrylates; rosin; modified rosin;terpene resin; phenolic resins; aliphatic or alicyclic hydrocarbonresins; aromatic petroleum resins; chlorinated paraffin; and paraffinwax. These compounds may be used alone or in combination.

The coloring agent may be a known one, such as carbon black, diazoyellow, phthalocyanine blue, quinacridone, carmine 6B, monoazo red orperylene.

Examples of the charge control agent are known ones such as Nigrosinedyes, fatty acid modified Nigrosine dyes, metallized Nigrosine dyes,metallized fatty acid modified Nigrosine dyes, chromium complexes of3,5-di-tert-butylsalicylic acid, quaternary ammonium salts,triphenylmethane dyes, and azochromium complexes.

To the toner of the present invention, there may be further added aflowing agent such as colloidal silica, aluminum oxide or titaniumoxide, and a lubricant comprising a fatty acid metal salt such as bariumstearate, calcium stearate or barium laurate.

The present invention will be described in more detail by reference toExamples and Comparative Examples.

CARRIER PREPARATION METHOD

Five parts by weight of a surface coating agent was coated onto 95 partsby weight of iron powder or ferrite powder of core substance, by meansof a spray dryer, to obtain a carrier for a dry two-component developer.

Example 1

95 Parts of iron powder (TEF-V150, Powdertech) was coated with asolution of 5 parts of T-745 (the polyolefin resin having a cyclicstructure recited in claim 1) in toluene by means of a spray dryer toobtain a carrier.

Example 2

95 Parts of iron powder (TEF-V150, Powdertech) was coated with a toluenesolution of 5 parts of a mixture of T-745 and S-8007 (the polyolefinresin having a cyclic structure recited in claim 1 that was prepared bymixing both compounds at a 60:40 ratio using a kneader) by means of aspray dryer to obtain a carrier.

Example 3

A mixture of T-745 and fluoro-acrylic graft polymer resin (LF-40, SokenKagaku) (the coating resin containing a cyclic polyolefin resin recitedin claim 2 that was prepared by mixing both compounds at a 50:50 ratiousing a kneader) was coated on the surface of iron powder (TEF-V150,Powdertech) in the same manner as in Example 1 to obtain a carrier.

Example 4

T-745-MO (the polyolefin resin having a cyclic structure recited inclaim 3 that was prepared by adding a carboxyl group to T-745 by meltair oxidation) was coated on the surface of iron powder (TEF-V150,Powdertech) in the same manner as in Example 1 to obtain a carrier.

Example 5

T-745-CL (the polyolefin resin having a cyclic structure recited inclaim 4 that was prepared by adding a peroxide to anethylene-norbornene-norbornadiene terpolymer to crosslink it) was coatedon the surface of iron powder (TEF-V150, Powdertech) in the same manneras in Example 1 to obtain a carrier.

Example 6

95 Parts of ferrite powder (a product of Powdertech) was coated with asolution of 5 parts of T-745 (the polyolefin resin having a cyclicstructure recited in claim 1) in toluene by means of a spray dryer toobtain a carrier.

Example 7

A mixture of T-745 and S-8007 (the polyolefin resin having a cyclicstructure recited in claim 1 that was prepared by mixing both compoundsat a 60:40 ratio using a kneader) was coated on the surface of ferritepowder (a product of Powdertech) in the same manner as in Example 6 toobtain a carrier.

Example 8

A mixture of T-745 and fluoro-acrylic graft polymer resin (LF-40, SokenKagaku) (the coating resin containing a cyclic polyolefin resin recitedin claim 2 that was prepared by mixing both compounds at a 50:50 ratiousing a kneader) was coated on the surface of ferrite powder (a productof Powdertech) in the same manner as in Example 6 to obtain a carrier.

Example 9

T-745-MO (the polyolefin resin having a cyclic structure recited inclaim 3 that was prepared by adding a carboxyl group to T-745 by fusingair oxidation) was coated on the surface of ferrite powder (a product ofPowdertech) in the same manner as in Example 6 to obtain a carrier.

Example 10

T-745-CL (the polyolefin resin having a cyclic structure recited inclaim 4 that was prepared by adding a peroxide to anethylene-norbornene-norbornadiene terpolymer to crosslink it) was coatedon the surface of ferrite powder (a product of Powdertech) in the samemanner as in Example 6 to obtain a carrier.

Comparative Example 1

Fluoro-acrylic polymer (LF-40, Soken Kagaku) was coated on the surfaceof iron powder (TEF-V150, Powdertech) in the same manner as in Example 1to obtain a carrier.

Comparative Example 2

Fluoro-acrylic polymer (LF-40, Soken Kagaku) was coated on the surfaceof ferrite powder (a product of Powdertech) in the same manner as inExample 6 to obtain a carrier.

Table 2 shows the fundamental properties of the polyolefin resins havinga cyclic structure that were used in the Examples.

                  TABLE 2                                                         ______________________________________                                        Product                                                                              Mw       Mn      i.v.    HDT    D    Tg                                ______________________________________                                        T745   7,000    3,800   0.19    less than                                                                            1.8  68                                      70                                                                        S-8007 70,000 35,000 0.25 or 70 or 2.0 80                                        more more                                                                  T745-MO 6,800 3,400 less than less than 2.0 78                                   0.25 70                                                                    T745-CL 12,000 3,400 less than less than 3.5 76                                  0.25 70                                                                  ______________________________________                                    

Fluoro Comb-shaped polymer L series LF-40, Soken Kagaku type

EVALUATIONS

The carriers prepared by the aforementioned carrier preparation methodwere each fed to a commercially available electrophotographic copier(Vivace 450, Fuji Xerox), and subjected to performance tests. Theresults are shown in Table 3. Table 3 shows that the carriers of theExamples are superior to the carriers of the Comparative Examples in allof the image sharpness and the anti-spent toner properties.

                  TABLE 3                                                         ______________________________________                                                         Charge                                                         Image control Anti-spent                                                      sharpness properties toner properties                                       ______________________________________                                        Ex.1    ◯                                                                              ◯                                                                          ◯                                     Ex.2 ◯ ◯ ◯                                Ex.3 ◯ Δ Δ                                            Ex.4 ◯ ◯ ◯                                Ex.5 ◯ ◯ ◯                                Ex.6 ◯ ◯ ◯                                Ex.7 ◯ ◯ ◯                                Ex.8 ◯ Δ Δ                                            Ex.9 ◯ ◯ ◯                                Ex.10 ◯ ◯ ◯                               Comp. X X X                                                                   Ex.1                                                                          Comp. Δ Δ Δ                                                 Ex.2                                                                        ______________________________________                                    

EVALUATION METHODS AND EVALUATION CRITERIA 1) Image Sharpness

The thin line resolving power and the maximum image density of the imageafter copying of 50,000 papers were compared with those of the imageobtained in the initial image. The change rate of less than 10% wasevaluated as ∘. The change rate of 10% or more but less than 20% wasevaluated as Δ. The change rate of 20% or more was evaluated as X.

2) Charge Control Properties

The initial charge of the toner and carrier, and their charge aftercopying of 30,000 papers were measured with Blowoff 500 of ToshibaChemical, and comparisons were made. The change rate of less than 5% wasevaluated as ∘. The change rate of 5% or more but less than 10% wasevaluated as Δ. The change rate of 10% or more was evaluated as X.

3) Anti-spent Toner Properties

Each of the carriers described in the Examples and the ComparativeExamples, and a toner of Fuji Xerox were put in a developer box inpredetermined amounts. These materials were stirred andtriboelectrically treated for one week. 5 grams each of the resultingtoner-deposited carriers was weighed. The carrier was put in water withsoap to remove the toner electrostatically adhering to the surface ofthe carrier. Only the magnetic carrier powder was withdrawn using amagnet. The magnetic powder was dipped in acetone to dissolve and removethe spent toner fusion bonded to the surface of the powder. The weightof the powder before acetone treatment and the weight of the powderafter acetone treatment were compared, and the change in weight wasexamined. The change rate of less than 0.2% was evaluated as ∘. Thechange rate of 0.2 to 0.5% was evaluated as Δ. The change rate of morethan 0.5% was evaluated as X.

The coated carrier for development of an electrostatically charged imageof the present invention has a coating resin, wherein the coating resinat least includes a polyolefin resin having a cyclic structure, and apolyolefin resin of a cyclic structure having an intrinsic viscosity(i.v.) of 0.25 dl/g or more, a heat distortion temperature (HDT) byDIN53461-B of 70° C. or higher, and a number average molecular weight of7,500 or more and a weight average molecular weight of 15,000 or more,as measured by GPC, is contained in an amount of less than 50% by weightbased on the entire coating resin. Thus, the coated carrier is excellentin the anti-spent toner effect and charge control properties. Adeveloper containing this carrier can achieve a high grade, sharp image.

What is claimed is:
 1. A coated carrier for development of anelectrostatically charged image, said coated carrier comprising carriercore particles coated with a coating resin; whereinsaid coating resin atleast includes a polyolefin resin having a cyclic structure; apolyolefin resin of a cyclic structure having an intrinsic viscosity(i.v.) of 0.25 dl/g or more, a heat distortion temperature (HDT) byDIN53461-B of 70° C. or higher, and a number average molecular weight of7,500 or more and a weight average molecular weight of 15,000 or more,as measured by GPC, is contained in an amount of less than 50% by weightbased on the entire coating resin; and said coating resin is used forcoating in an amount of 1 to 30% by weight based on the carrier coreparticles.
 2. The coated carrier of claim 1, wherein said coating resinconsists of 1 to 100 parts by weight of a polyolefin resin having acyclic structure, and 0 to 99 parts by weight of at least one resinselected from fluoro-acrylic graft polymer, cellulose butyl acetate, andsilicone resins.
 3. The coated carrier of claim 1, wherein saidpolyolefin resin having a cyclic structure has at least one functionalgroup selected from the group consisting of a carboxyl group, a hydroxylgroup and an amino group.
 4. The coated carrier of claim 1, wherein saidpolyolefin resin having a cyclic structure has a structure crosslinkedwith metallic ions or dienes.
 5. The coated carrier of claim 1, whereinthe polyolefin resin having a cyclic structure is a colorless andtransparent copolymer of an alpha olefin obtained from a polymerization.6. The coated carrier of claim 1, wherein the polyolefin resin having acyclic structure has a high light transmittance and is selected from thegroup consisting of ethylene, propylene or butylene with an alicycliccompound having a double bond, such as cyclohexene or norbornene.